MAX3766 Maxim, MAX3766 Datasheet - Page 13

• Manufacturer Part Number: MAX3766
• Description: 622Mbps LAN/WAN Laser Driver with Automatic Power Control and Safety Shutdown
• Manufacturer: Maxim

Figure 7. Example Laser Compensation
The MAX3766’s junction temperature must be kept
below +150°C at all times. Calculate total power dissi-
pated on the MAX3766 by laser power as follows:
Power = V
where I
R
is the typical laser forward voltage.
Junction temperature = power (Watts) 110 (°C/W).
Many MAX3766 specifications relate to output current
amplitude. When working with fiber optic transmitters,
the output is normally expressed in terms of average
optical power and extinction ratio (Figure 8). Table 2
lists relations that are helpful in converting optical
power to output signal amplitude when designing with
the MAX3766. The relations are true if the average duty
cycle of the input data is 50%.
The MAX3766’s data inputs must be biased externally.
Refer to Figure 9 for common input terminations.
The International Electrotechnical Commission (IEC)
determines standards for hazardous light emissions
from fiber optic transmitters. Specification IEC 825
defines the maximum light output for various hazard
levels. The MAX3766 provides features that aid compli-
ance with IEC 825.
__________Applications Information
BIASMAX
Automatic Power Control and Safety Shutdown
BIAS
- (I
, I
CC
MOD
MOD
is the maximum bias current allowed by
(I
CC
Calculate Power Consumption
/ 2 + I
is the AC modulation current, V
______________________________________________________________________________________
+ I
BIAS
UNCOMPENSATED
OVERCOMPENSATED
BIAS
Laser Safety and IEC 825
CORRECTLY COMPENSATED
500ps/div
Optical Power Relations
+ I
622Mbps LAN/WAN Laser Driver with
) V
MOD
LASER
Input Terminations
)
.
LASER
A common safety requirement is single-point fault toler-
ance, whereby one unplanned short, open, or resistive
connection does not cause excess light output. When
the MAX3766 is used in the latched shutdown configu-
ration, as shown in Typical Application Circuits , the cir-
cuit responds as shown in Table 3.
Using the MAX3766 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Each customer must determine the level
of fault tolerance required by their application, recogniz-
ing that Maxim products are not designed or authorized
for use as components in systems intended for surgical
implant into the body, for applications intended to sup-
port or sustain life, or for any other application where the
failure of a Maxim product could create a situation
where personal injury or death may occur.
Figure 8. Optical Power Relations
Table 2. Optical Power Definitions
PARAMETER
Average
Power
Extinction
Ratio
Optical Power
of a “1”
Optical Power
of a “0”
Signal
Amplitude
OPTICAL
POWER
P
AVE
P1
P0
SYMBOL
P
P
INPUT
P1
P0
AVE
r
e
P
P
r = 1 / P0
P
P
e
INPUT
1 2
AVE
0 2
P
= P0 + P1
P
P
AVE
AVE
P1 - P0 2P
RELATION
r
/
e
r
e
r
e
1
/ 2
1
TIME
AVE
r
r - 1
e
e
13
1